1. Field of the Invention
The present invention relates to a magneto-resistive tunnel junction head for reading the magnetic field intensity from a magnetic recording medium or the like as a signal and, in particular, to a magneto-resistive tunnel junction head having common leads and shields and suitable for ultra-high density magnetic recording.
2. Description of the Prior Art
MR sensors based on the anisotropic magneto-resistance (AMR) or spin-valve (SV) effect are widely known and extensively used as read transducers in magnetic recording. MR sensors can probe the magnetic stray field coming out from transitions recorded on a recording medium by the resistance changes of a reading portion formed of magnetic materials. AMR sensors have quite a low resistance change ratio xcex94R/R, typically from 1 to 3%, whereas the SV sensors have a xcex94R/R ranging from 2 to 7% for the same magnetic field excursion. The SV magnetic read heads showing such high sensitivity are progressively supplanting the AMR read heads to achieve very high recording density, namely over several Giga bits per square inch (Gbits/in2).
Recently, a new MR sensor has attracted attention for its application potential in ultra-high density recording. Magneto-resistive tunnel junctions (MRTJ, or synonymously referred to as TMR) are reported to have shown a resistance change ratio xcex94R/R over 12%. Although it has been expected that TMR sensors replace SV sensors in the near future as the demand for ultra-high density is ever growing, an application to the field of the magnetic heads has just started, and one of the outstanding objects is to develop a new head structure, which can maximize the TMR properties. Great efforts of developments are still needed to design a new head structure since TMR sensors operate in CPP (Current Perpendicular to the Plane) geometry, which means that TMR sensors requires the current to flow in a thickness direction of a laminate film.
In a basic SV sensor which has been developed for practical applications, two ferromagnetic layers are separated by a non-magnetic layer, as described in U.S. Pat. No. 5,159,513. An exchange layer (FeMn) is further provided so as to be adjacent to one of the ferromagnetic layers. The exchange layer and the adjacent ferromagnetic layer are exchange-coupled so that the magnetization of the ferromagnetic layer is strongly pinned (fixed) in one direction. The other ferromagnetic layer has its magnetization which is free to rotate in response to a small external magnetic field. When the magnetization""s of the ferromagnetic layers are changed from a parallel to an antiparallel configuration, the sensor resistance increases and a xcex94R/R in the range of 2 to 7% is observed.
In comparison between the SV sensor and the TMR sensor, the structure of the TMR is similar to the SV sensor except that the non-magnetic layer separating the two ferromagnetic layers is replaced by a tunnel barrier layer being an insulating layer and that the sense current flows perpendicular to the surfaces of the ferromagnetic layers. In the TMR sensor, the sense current flowing through the tunnel barrier layer is strongly dependent upon a spin-polarization state of the two ferromagnetic layers. When the magnetization""s of the two ferromagnetic layers are antiparallel to each other, the probability of the tunnel current is lowered, so that a high junction resistance is obtained. On the contrary, when the magnetization""s of the two ferromagnetic layers are parallel to each other, the probability of the tunnel current is heightened and thus a low junction resistance is obtained.
U.S. Pat. No. 5,729,410 discloses an example wherein a TMR sensor (element) is applied to a magnetic head structure. The TMR sensor is sandwiched between two parallel electrical leads (electrodes), that are in turn sandwiched between first and second insulating gap layers of alumina or the like to form a read gap. A pair of magnetic shield layers are further formed to sandwich therebetween the first and second insulating gap layers.
However, as described above, the conventional TMR head has a structure wherein the pair of electrode layers, the pair of gap layers and the pair of shield layers are stacked in turn to sandwich the TMR multilayered film. As a result, the read gap is enlarged at a head end surface, i.e. an ABS (Air Bearing Surface) of the head, confronting against a magnetic recording medium. Thus, such kind of TMR head design is handicapped for application to high-density recording. Moreover, the biasing efficiency of this structure is quite poor due to the separation between the free layer and the permanent magnets. If the permanent magnets are formed in an overlapping manner on the TMR film, a strong decrease of the TMR ratio is yet expected due to a large difference of the junction resistance in the regions below and in between the permanent magnets.
The present invention has been made under these circumstances and has an object to provide a magneto-resistive tunnel junction (TMR) head which has an improved new electrode structure so as to be readily adaptable to high-density recording.
Another object of the present invention is to provide a magneto-resistive tunnel junction head with high biasing efficiency and no reduction in TMR ratio to ensure a high and stable head output for adaptation to ultra high-density recording.
For solving the foregoing problems, according to one aspect of the present invention, there is provided a magneto-resistive tunnel junction head comprising a tunnel multilayered film having a tunnel barrier layer, a ferromagnetic free layer and a ferromagnetic pinned layer such that the tunnel barrier layer is held between the ferromagnetic free layer and the ferromagnetic pinned layer; and a common lead and shield layer electrically contacted with at least one of opposite sides in a laminate direction of the tunnel multilayered film, the common lead and shield layer serving both as an electrode for allowing a sense current to flow through the tunnel multilayered film and as a magnetic shield layer, wherein the common lead and shield layer extends to a rear portion of the tunnel multilayered film from an air bearing surface (ABS) so that a part of the common lead and shield layer located at the rear portion of the tunnel multilayered film serves as a back flux guide for improving a read output.
It is preferable that the common lead and shield layers are electrically contacted with the opposite sides of the tunnel multilayered film in the laminate direction thereof such that one of the common lead and shield layers extends to the rear portion of the tunnel multilayered film from the air bearing surface (ABS) so that the part of the one of the common lead and shield layers located at the rear portion of the tunnel multilayered film serves as the back flux guide for improving the read output.
It is preferable that an electrically conductive, non-magnetic gap layer is provided between the common lead and shield layer and the tunnel multilayered film.
It is preferable that the common lead and shield layer is made of a material selected from NiFe, Sendust, CoFe and CoFeNi.
It is preferable that the gap layer comprises a layer made of a material selected from Cu, Al, Ta, Au, Cr, In, Ir, Mg, Rh, Ru, W, Zn or an alloy thereof.
It is preferable that the gap layer has a thickness of 50 to 700 xc3x85.
It is preferable that the gap layer is made of a highly anticorrosive material and selected from Ta, Rh and Cr.
It is preferable that the ferromagnetic free layer of the tunnel multilayered film is connected, at longitudinally opposite ends thereof, with biasing means so that a biasing magnetic field is applied to the ferromagnetic free layer in a longitudinal direction thereof, and that the ferromagnetic free layer has a length in the longitudinal direction which is set greater than a longitudinal length of the ferromagnetic pinned layer such that the ferromagnetic free layer has at the opposite ends thereof extended portions each extending beyond corresponding one of longitudinal opposite ends of the ferromagnetic pinned layer.
It is preferable that biasing means located at longitudinal opposite ends of the ferromagnetic free layer are magnetically contacted with upper or lower portions of extended portions at the opposite ends of the ferromagnetic free layer, and that each of the biasing means is located with a predetermined space (D) from corresponding one of longitudinal opposite ends of the ferromagnetic pinned layer.
It is preferable that the space (D) is set to no less than 0.02 xcexcm.
It is preferable that the space (D) is set to no less than 0.02 xcexcm and no greater than 0.3 xcexcm.
It is preferable that the space (D) is set to no less than 0.02 xcexcm and less than 0.15 xcexcm.
It is preferable that the ferromagnetic free layer has a thickness of 20 to 500 xc3x85.
It is preferable that the tunnel multilayered film has a multilayered film detection end surface constituting the air bearing surface (ABS).
It is preferable that the ferromagnetic free layer is a synthetic ferrimagnet.
It is preferable that the ferromagnetic pinned layer is in the form of a pair of ferromagnetic layers antiferromagnetically coupled via a non-magnetic layer.
It is preferable that each of the biasing means is made of a highly coercive material or an antiferromagnetic material, or in the form of a laminate body having an antiferromagnetic layer and at least one ferromagnetic layer.
It is preferable that a pinning layer for pinning magnetization of the ferromagnetic pinned layer is stacked on a surface of the ferromagnetic pinned layer remote from a side thereof abutting the tunnel barrier layer.
It is preferable that longitudinal opposite ends of the tunnel multilayered film are insulated by insulating layers.